Virginia Worthington

Summer 2002
Virginia Worthington, Ph.D., of Nutrikinetics in Washington, D.C., shared her research showing nutritional differences between organic and conventional produce at Spring Growth. English photo.

Dr. Virginia Worthington is a nutritionist who holds a doctorate from Johns Hopkins University and is now a nutritional consultant with Nutrikinetics of Washington, D.C. She has compared studies of nutritional aspects of organic versus conventional foods and presented some of the results in her paper, “Nutritional Quality of Organic Versus Conventional Fruits, Vegetables, and Grains,” J. Alternative and Complementary Med., Vol. 7, No. 2, 2001, pp. 161-173. She spoke about her findings, as well as additional information on pesticides and animal studies, at MOFGA’s Spring Growth Conference, “You Are What You Eat,” on March 23, 2002.

Worthington began by summarizing her findings: that the nutrient content of crops is affected by fertilizers and pesticides; that organic crops have a greater nutrient density than those fertilized conventionally; that animals fed organic feed are healthier than those receiving conventional feed; and that limited data exist on the health effects of organic foods on humans.

Why don’t we hear much about these differences, Worthington asked? “When conventional fertilizers first came on the scene, people didn’t keel over and die immediately or get very ill. So the effects of conventional foods were not huge and immediate in healthy adults. If they were bad, it was something like tobacco — it takes many years to see the effects. But health does degenerate over a long period from smoking.” Such differences don’t show up in short-term studies.

Also, differences can appear to be small and not worth pursuing. Her own data from when she worked at USDA showed, for example, that organic peppers had 1.2 mg/g of vitamin C, while conventional had 1.1 mg/g. “A difference of 0.1 mg is really a tiny amount. You look at that and look at what you can buy at the drugstore —1000 mg in a pill — so the amount in the green pepper seems pretty minuscule. This didn’t give people a lot of reason to investigate further.

“I was like everybody else,” Worthington continued, until she summarized data from numerous studies on nutrient concentrations in organic vs. conventional foods for an editor several years ago. She made a table, and for each study and each nutrient, she used either an up arrow, indicating that organic had more of that nutrient than conventional in that particular study; a down arrow, indicating less; or an equal sign, indicating no difference. She noticed that organic foods often had more vitamin C and smaller concentrations of nitrates than conventional. “I was just eyeballing the data.” Then she did a more precise review with actual numbers and found significant differences.

Effects of Fertilizers

Worthington looked at studies of farming systems and nutritional composition of the foods from those systems. One study, for example, compared tomatoes grown in Lancaster, Penn., in 1988. A tomato raised organically had 30 mg of vitamin C, while one raised conventionally had 25 milligrams. She put such numbers from all of the studies she could find into the computer and had it do the appropriate statistics to determine whether organic foods differed significantly from conventional. She had enough data to do the statistics on 12 nutrients and two vitamins (beta carotene and vitamin C) and found the following significant increases in organic foods:

Vitamin C – 27.0%

Iron –21.1%

Magnesium – 29.3%

Phosphorus – 13.6%

In addition, nitrate concentrations were 15.1% lower.

Worthington noted that these figures could change as more data are generated, but they do show differences. When her study was criticized for the statistical methods used, she used other methods as well and found the same. “These are statistically robust results.”

She also found trends that were not statistically different but may be as more data become available. They included: less but better quality protein in organic foods; greater amounts of other nutritionally significant minerals; and lower amounts of heavy metals.

These data agree with those showing a decline in the nutrient content of foods over the last several years. Data from the USDA and its equivalent in Britain showed the following:

Percent Decline in Mineral Content of U.S. and British Crops in the Last Sixty Years

U.S. 1963-1992 Britain 1936-1987
Mineral (13 fruits & vegs.) (20 fruits & 20 vegs.)
Calcium -29 -19
Magnesium -21 -35
Sodium N/A -43
Potassium -6 -14
Iron -32 -22
Copper N/A -81

N/A, not analyzed

U.S. data from Bergner, P., The Healing Power of Minerals, Special Nutrients and Trace Elements, Rocklin, CA: Prima Publishing Co., 1997:46-75.

British data from Mayer, A-M, “Historical changes in the mineral content of fruits and vegetables: A cause for concern?” Br. Food J., 1997; 99:207-11.

What we know about soil dynamics, fertilizers and plant physiology all support Worthington’s findings, she said. Organic agriculture got its name because we add organic matter to the soil. Through compost, animal manures and green manures, we feed the soil microbes, which make many compounds that help plants. For example, microbes can break down rocks and secrete compounds that “hook onto” minerals and make those minerals more available to plant roots. “So we would expect to see more minerals in organically treated soil than one that was fertilized conventionally, with no organic matter added.”

Also, microbes can make B vitamins. “Not many studies compare B vitamins in organic and conventional foods,” said Worthington, “partly because if s difficult to analyze B vitamins in the lab. And B vitamins have been out of favor as people have studied antioxidants, such as vitamins C and E, more.” However, plants can absorb B vitamins from the soil. “One study in Switzerland showed that when they put animal manures into the soil, vitamin B12 will persist in the soil for long periods in high quantities, and plants can take up detectable quantities of vitamin B12. For many years in nutrition, it was absolute dogma that there was no B12 in crops, in plant foods. If organically grown foods could be analyzed for B12, possibly we could find some significant differences in how we view foods and agriculture.”

Third, organic matter breaks down slowly so that plants are presented with nutrients throughout the growing season. When it’s hot and plants are growing fast, microbes, likewise, are working more. When it’s cold, the opposite happens. So plants, microbes and the weather operate in synch with one another. “Microbes provide plants with the amounts of nutrients that are appropriate for the prevalent conditions,” Worthington explained. “In contrast, conventional fertilizers dissolve rapidly in the soil water and present plants with a lot of nutrients all at one time.” As a result, high concentrations of nitrogen in the soil will produce more and worse quality protein, because the plant is presented with a lot of nitrogen at once and it has to do something with it. “So it makes more protein (a high nitrogen product) and less carbohydrates (vitamin C is made from carbohydrates). After it makes enough protein for its metabolic needs, it then makes storage proteins, such as gluten in wheat and zein in corn. That’s where you get the lower quality. And when it has even more nitrogen, it makes nitrate” – which is a toxin, carcinogen, inhibits thyroid function and can cause blue baby syndrome.

Likewise, when potassium fertilizer is in excess, phosphorus, magnesium and calcium concentrations in the plant may be reduced, because plants take up potassium preferentially to magnesium and calcium; and because phosphorus tends to be taken up into plants along with magnesium, so if magnesium uptake is depressed, so is phosphorus uptake.

Some phosphate fertilizers, trace mineral fertilizers and liming materials come from industrial wastes and can contain harmful heavy metals. “In fact, some trace metal fertilizers are classified as toxic wastes by the EPA,” said Worthington. These can increase the concentrations of heavy metals in soils and plants.

“So what we know about fertilizer effects agrees with what we saw in the nutrient analyses,” said Worthington. Also, when crops are fertilized with synthetic nitrogen fertilizers, you often get more water taken into the crop as N uptake increases. That water dilutes essential nutrients. “You may get a better yield, but some of that increased yield will be water,” said Worthington.

Effects of Pesticides

The effects of insecticides on the nutrient composition of crops are not well studied, said Worthington, but effects of herbicides are because herbicides are designed to kill plants. “So they’re looking at how they kill plants.” Worthington cited a study called “Effects of Selected Pesticides on Nutritive Composition of Fruits and Vegetables” that was presented to the Human Nutrition Division of the USDA’s Agricultural Research Service in 1972. The bulk of the report showed the effects of triazine herbicides on protein. “They thought they might be able to use herbicides to increase the nutrient value in foods.”

The triazine herbicides work by inhibiting photosynthesis, Worthington continued. These can result in more protein in the crop, but that protein lacks quality; they can result in less beta-carotene; and in less tocopherol (vitamin E). The bleaching herbicides, such as diuron, can reduce beta-carotene. Sulfonylurea herbicides can produce poorer protein quality (i.e., fewer branched chain amino acids). And Roundup interferes with the synthesis of the amino acid tyrosine, and thus with bioflavinoids and phytoestrogens, when applied to non-genetically engineered crops.

Effects on Diets

“So soil and pesticides can affect the nutrient content. How does this affect our diet?” Worthington asked. According to the USDA food pyramid, “we’re told to eat five fruits and vegetables a day.” In the data she studied, five vegetables were studied more than others: cabbage, carrots, potatoes, lettuce and spinach. “What would happen if somebody ate those as their five servings of vegetables?” she wondered. How would their nutrient intake differ in one day if they ate organic vs. conventional vegetables? She found that the nutrient content of an organic and conventional diet for one day would contain the following from these five vegetables:

Vitamin C Iron Magnesium Phosphorus
Diet mg mg mg mg
Organic 89.2 3.7 80.0 124.0
Conventional 67.9 3.0 68.6 111.8

So, each day, the organic diet would provide small additional amounts of these nutrients. Looking at vitamin C, Worthington noted that the amount of that nutrient in the organic vegetables met the RDA for vitamin C, while the amount in the conventional did not. “The RDA for vitamin C has been raised twice in the last 30 years,” she said, “so that alone, that small additional quantity of vitamin C, could have some health giving effects.”

Also, when nutrient interactions are considered, small effects become larger. Referring to her own data showing just a 0.1 mg difference in vitamin C in an organic vs.conventional pepper, she noted that vitamin C helps increase the absorption of iron; helps folic acid; cleans up vitamin E so that it can be used again, and vitamin E in turn helps vitamin A, which spares iron … So by taking in a little more vitamin C, “it’s as though you took in a little more” vitamin E, A, folic acid and iron as well. Small differences in the amount of one nutrient “can have greater effects than you would expect.”

Next Worthington said that she looked at about 15 animal studies comparing organic with conventional feed. About three were done in ways that would mask differences. The others showed better health among animals fed organically – in fertility (egg production and sperm motility); survival of the young; number of illnesses; and recovery from illnesses. A German study looked at two groups of rabbits, for instance. When they were moved from lab chow to organic feed, they maintained their fertility over three generations, while fertility declined in rabbits moved to conventional chow. A second German study showed that among rabbits fed conventional food or lab chow, about half the young survived, while nearly three quarters survived among rabbits fed organically. Another study looked at the fertility of bulls on a farm in Germany by measuring how many days sperm stayed motile. Worthington showed the following data:

1957 – 4 days

1958 – 4 days

1959 – 2 days

1960 – 2 days

1961 – 1 day

1962 – 3 days

The 1957 and 1958 rates occurred before conventional fertilizers were used on the farm. From 1959 to 1961, pastures were fertilized conventionally; in 1961, the farm had to destroy two bulls because iiey weren’t producing any sperm at all. In 1962, the farm brought in food from a neighboring organic farm.


Worthington repeated the conclusions that she stated at the beginning of her talk: Nutrient content can be affected by fertilizers and pesticides; nutrient density is greater in organic crops; and animals fed organically have better health. On the other hand, the animals fed conventionally “didn’t keel over and die, but had fertility problems and didn’t recover as well when they got sick. I have to remind you,” she said, “there is a big industry in this country for fertility of humans. Our food supply could be contributing to all of the health problems we’re seeing. In a sense, our farmers are the first line officers in our public health service.”

They may also present first-line research subjects. Worthington cited a Danish study in which farmers were classified according to how much organic food they ate, then their sperm was studied. (Sperm can respond to treatments and be studied quickly, because it is made and is then gone in about a week.) According to the strictest measure of sperm health – the health of the entire sperm – the researcher could see that the more organic foods a farmer ate, the more sperm were in good health. “There was a direct correlation,” said Worthington. (Juhler, R.K., Larsen, S.B., Meyer, O., Jensen, N.D., Spano, M., Giwercman, A., Bonde, J.P., “Human semen quality in relation to dietary pesticide exposure and organic diet.” Arch. Environ. Contam. Toxicol., 1999; 37:415-423.)

You can request reprints of “Nutritional Quality of Organic Versus Conventional Fruits, Vegetables, and Grains” by emailing Dr. Worthington at [email protected].

– Jean English

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